Assemblies and methods for processing zinc-bearing materials

Abstract

A process for separating and recovering a desired metal as metal oxide from raw material is provided. The process includes placing the raw material and a reductant in a container to form a reducing microclimate within the container. A housing having an oxidizing atmosphere is heated to maintain a temperature zone within the housing at a heating temperature sufficient to expose the raw material in the container to a reaction temperature. The container containing the raw material is conveyed through the temperature zone in the housing to expose the raw material and the reductant to the reaction temperature wherein the metal oxide is reduced to a gaseous metal that exits the container. Once outside the container, the gaseous metal is exposed to the oxidizing atmosphere of the temperature zone wherein the desired metal is oxidized to metal oxide and the metal oxide is collected. In preferred embodiments, the raw material is EAF dust and the desired metal is zinc. In one specific embodiment, the process also includes maintaining a second temperature zone in the housing at a metal halide vaporization temperature, which is lower than the heating temperature. A flow of air is applied through the housing in a direction that is opposite to a direction of travel of the container during the conveying step, whereby a metal halide in the raw material is volatilized to a volatilized metal halide when the container is conveyed through the second heating zone. The volatilized metal halide is then collected.

What is claimed is:  
     
       1. A process for separating and recovering a desired metal as metal oxide from raw material containing metal oxides, comprising the steps of: 
       placing the raw material and a reductant in a container to form a reducing microclimate within the container;  
       heating a housing to maintain a temperature zone within the housing at a heating temperature sufficient to expose the raw material in the container to a reaction temperature that is higher than the boiling point of the desired metal, the temperature zone having an oxidizing atmosphere;  
       conveying the container containing the raw material through the temperature zone in the housing to expose the raw material and the reductant to the reaction temperature wherein the metal oxide is reduced to a gaseous metal that exits the container;  
       exposing the gaseous metal to the oxidizing atmosphere of the temperature zone wherein the desired metal is oxidized to metal oxide; and  
       collecting the metal oxide.  
     
     
       2. The process of  claim 1  further comprising: 
       maintaining a second temperature zone in the housing at a metal halide vaporization temperature, the metal halide temperature being lower than the heating temperature;  
       applying a flow of air through the housing in a direction that is opposite to a direction of travel of the container during the conveying step, whereby a metal halide in the raw material is volatilized to a volatilized metal halide when the container is conveyed through the second heating zone; and  
       collecting the volatilized metal halide.  
     
     
       3. The process of  claim 2  wherein the metal halide vaporization temperature is between about 1600° F. and about 2000° F. 
     
     
       4. The process of  claim 3  wherein the metal halide vaporization temperature is about 1800° F. 
     
     
       5. The process of  claim 2 , further comprising mixing a halide with the raw material and the reductant, whereby the halide reacts with metal compounds in the raw material to form metal halides, the metal halides having a boiling point that is at least as low as the metal halide vaporization temperature. 
     
     
       6. The process of  claim 2  wherein the halide is a chloride. 
     
     
       7. The process of  claim 1  wherein the reductant contains carbon. 
     
     
       8. The process of  claim 7  wherein the reductant is coke or coal. 
     
     
       9. The process of  claim 1  wherein the reductant contains a metal. 
     
     
       10. The process of  claim 9  wherein the reductant includes aluminum. 
     
     
       11. The process of  claim 1  wherein the heating step includes maintaining the temperature zone at an oxygen level of at least about 2.0 %. 
     
     
       12. The process of  claim 1 , further comprising the step of: 
       mixing the raw material with the reductant before the placing step.  
     
     
       13. The process of  claim 1  wherein the heating step includes maintaining the partial pressure of carbon monoxide to carbon dioxide within the container at a ratio that is sufficient to achieve a reducing microclimate within the container. 
     
     
       14. The process of  claim 1 , further comprising the step of: 
       blending the raw material and the reductant with a binding agent to form a blend before the placing step; and  
       forming the blend into formed units.  
     
     
       15. The process of  claim 14  wherein the binding agent includes water. 
     
     
       16. The process of  claim 14  wherein the placing step includes loading the formed units in the bed to a depth of between about 1.0 inches (2.5 cm) to about 14.0 inches (35.5 cm). 
     
     
       17. The process of  claim 1  wherein the conveying step includes conveying the container on a kiln car and the collecting step includes collecting the metal oxide from the kiln car as the kiln car exits the housing. 
     
     
       18. A process for separating and recovering zinc oxide and iron-rich product from electric arc furnace dust containing zinc oxide and iron-rich materials, comprising: 
       placing the electric arc furnace dust and a reductant in a container to form a reducing microclimate;  
       heating a housing to maintain a temperature zone at a heating temperature sufficient to expose the raw material in the container to a reaction temperature that is higher than the boiling point of zinc metal, the temperature zone having an oxidizing atmosphere;  
       conveying the container containing the electric arc furnace dust and the reductant through the temperature zone in the housing to expose the electric arc furnace dust and the reductant to the reduction temperature wherein zinc oxide in the electric arc furnace duct is reduced to zinc metal gas that exits the container;  
       exposing the zinc metal gas to the oxidizing atmosphere of the temperature zone wherein the vaporized zinc metal is oxidized to zinc oxide in the housing; and  
       collecting the zinc oxide from the housing and collecting the iron-rich product from the container.  
     
     
       19. The process of  claim 18  further comprising: 
       maintaining a second temperature zone in the housing at a metal halide vaporization temperature, the metal halide temperature being lower than the heating temperature;  
       applying a flow of air through the housing in a direction that is opposite to a direction of travel of the container during the conveying step, whereby a metal halide in the raw material is volatilized to a volatilized metal halide when the container is conveyed through the second heating zone; and  
       collecting the volatilized metal halide.  
     
     
       20. The process of  claim 19  wherein the metal halide vaporization temperature is between about 1600° F. and about 2000° F. 
     
     
       21. The process of  claim 20  wherein the metal halide vaporization temperature is about 1800° F. 
     
     
       22. The process of  claim 19  wherein the halide is a chloride. 
     
     
       23. The process of  claim 18  wherein the reductant contains carbon. 
     
     
       24. The process of  claim 23  wherein the reductant is coke or coal. 
     
     
       25. The process of  claim 19 , further comprising mixing a halide with the raw material and the reductant, whereby the halide reacts with metal compounds in the raw material to form metal halides, the metal halides having a boiling point that is at least as low as the metal halide vaporization temperature. 
     
     
       26. The process of  claim 18  wherein the reaction temperature is at least about 900° C. (1652° F.). 
     
     
       27. The process of  claim 26  wherein the reaction temperature is between about 1218° C. (2225° F.) and about 1649° C. (3000° F.). 
     
     
       28. The process of  claim 18  wherein the heating step includes maintaining the partial pressure of carbon monoxide to carbon dioxide within the container at a ratio that is sufficient to achieve a reducing microclimate within the container. 
     
     
       29. The process of  claim 18  wherein the heating step includes maintaining the temperature zone at an oxygen level of at least about 2.0 %. 
     
     
       30. The process of  claim 18  wherein the conveying step includes conveying the container through the temperature zone in about one to about twenty hours. 
     
     
       31. The process of  claim 30  wherein the conveying step includes conveying the container through the temperature zone in about ten to about fourteen hours. 
     
     
       32. The process of  claim 18 , further comprising the step of: 
       mixing the raw material with the reductant before the placing step.  
     
     
       33. The process of  claim 32 , further comprising the step of: 
       blending the raw material and the reductant with a binding agent to form a blend before the placing step; and  
       forming the blend into formed units.  
     
     
       34. The process of  claim 33  wherein the placing step includes loading the container with blend so that the container has a vent area/material volume ratio of at about 0.25 feet2 of vent area per cubic foot of blend within the bed. 
     
     
       35. The process of  claim 34  wherein the raw material is present in the blend in an amount between about 65 wt % and about 80 wt %, the reductant is present in an amount between about 10 wt % and about 20 wt % and the binding agent is present in an amount between about 10 wt % and about 20 wt %. 
     
     
       36. The process of  claim 35  wherein the binding agent includes water present in the amount of about 3.0 wt % to about 20.0 wt %. 
     
     
       37. The process of  claim 18  wherein the reductant is present in an amount sufficient to completely reduce the zinc oxide present in the electric arc furnace dust. 
     
     
       38. The process of  claim 33  wherein the raw material is present in the blend in an amount of about 85 wt %, the reductant is present in an amount of about 15 wt %. 
     
     
       39. The process of  claim 33  wherein the raw material is present in the blend in an amount of about 84.5 wt %, the reductant is present in an amount of about 12.0 wt % and the binding agent is present in an amount of about 3.0 wt %. 
     
     
       40. The process of  claim 33  wherein the placing step includes loading the formed units in the bed to a depth of between about 1.0 inches (2.5 cm) to about 14.0 inches (35.5 cm). 
     
     
       41. The process of  claim 40  wherein the placing step includes loading the formed units in the bed to a depth of between about 5.0 inches (12.7 cm) to about 9.0 inches (22.9 cm). 
     
     
       42. The process of  claim 41  wherein the placing step includes loading the briquettes or pellets in the bed to a depth of about 6.0 inches (15.2 cm). 
     
     
       43. The process of  claim 18  wherein the conveying step includes conveying the container on a kiln car and the collecting step includes collecting the metal oxide from the kiln car as the kiln car exits the tunnel. 
     
     
       44. A process for treating electric arc furnace dust, comprising: 
       placing the electric arc furnace dust and a reductant containing carbon in a container to form a reducing microclimate having a partial pressure of carbon monoxide to carbon dioxide sufficient to reduce metal oxides in the electric arc furnace dust to a corresponding metal;  
       heating a housing to maintain a temperature zone at a heating temperature sufficient to expose the raw material in the container to a reaction temperature that is higher than the boiling point of zinc metal, the temperature zone having an oxidizing atmosphere;  
       conveying the container containing the electric arc furnace dust and the reductant through the housing to expose the electric arc furnace dust and the reductant to the reaction temperature wherein zinc oxide in the raw material is reduced to zinc metal gas that exits the container;  
       exposing the zinc metal gas to the oxidizing atmosphere of the temperature zone wherein the vaporized zinc metal is oxidized to zinc oxide in the housing;  
       collecting the zinc oxide from the housing, the zinc oxide collected from the housing having less than about 0.06% impurities and collecting the iron-rich product from the container, the iron-rich product having between less than about 1.0% zinc and less than detectable levels of lead and cadmium; and  
       collecting volatilized halogens of lead and cadmium in a baghouse.  
     
     
       45. The process of  claim 44  wherein the iron-rich product has between about 0.02% to about 1.0% zinc.